Arrangement for automated fabrication of fiber optic devices

ABSTRACT

Fiber optic devices are manufactured in an automated environment using a combination of clamps to secure the optical fibers and movable gripping devices that transport the optical fiber during the fabrication process while maintaining control of the ends of the optical fibers. An optical fiber from a spool is removed by a despooling arm having a gripping device, and moveable grippers thread the optical fiber into a set of clamps and place the end of the optical fiber in a clamp designed to splice the fiber optic end to a lead of a testing device. The fiber optic device is formed by dynamically controlling the heating and pulling process based on detected coupling ratios, and hermetically sealed while secured within the clamps. The sealed fiber optic device is moved for testing or packaging using a transport arm having a series of clamps to maintain the position of the fiber optic device and the ends of the leads of the fiber optic device.

This application is a division of application Ser. No. 08/763,122 filedDec. 10, 1996.

TECHNICAL FIELD

The present invention relates to manufacturing techniques for makingfiber optic devices from optical fibers, specifically to the fabricationof fiber optic couplers.

BACKGROUND ART

Fiber optic couplers are used as optical beam splitters between two ormore fibers. Fused biconical tapered couplers are formed generally byplacing two bare single mode fibers in contact with each other, addingtension to the fibers, and heating the fibers using a heat source, forexample a flame. As the fibers soften, they fuse together to form thefused biconical tapered coupler.

The conventional manufacture of fiber optic devices such as the fusedbiconical tapered coupler suffer from the fundamental problem thatmanual handling by technicians or operators introduces variations to themanufacturing process. Depending on the fiber optic device being formed,a considerable amount of error may be introduced by the handling of anoptical fiber by an operator or technician. For example, conventionalformation of a coupler includes removing of an outer coating from two ormore optical fibers and placing the exposed optical fibers in contactwith each other. The fibers may be twisted together, depending on theparticular technique used to manufacture the coupler. The fibers arethen fused together by heat, as the fibers are placed under tension byslowly and carefully pulling them apart at a predetermined rate. Giventhe delicate nature of optical fibers, the manufacture of optical fibercouplers requires highly skilled and trained technicians.

An additional problem with conventional manufacturing techniques is thatthe optical characteristics of the fiber optic devices duringmanufacture are uncontrollable. Skilled technicians with experience fromtrial and error have been needed to anticipate the opticalcharacteristics of a fiber optic device during manufacture. For example,technicians making fused biconical tapered couplers would recognize thata jump in the detected coupling ratio occurs when a heat source issuddenly removed from the heated optical fibers. Technicians wouldattempt to anticipate the jump in the detected coupling ratio such thatthe heat source, when removed, would cause the detected coupling ratioto jump to the desired level. Hence, the yield of the manufacturingprocess would be unpredictable and entirely dependent on the individualtechnician's expertise.

U.S. Pat. No. 5,386,490 to Pen et al., incorporated in its entiretyherein by reference, discloses a workstation for manufacturing a couplerbetween at least two optical fibers. A technician threads an opticalfiber from an optical fiber spool into the clamping assembly. Thetechnician is also needed to terminate the bare fiber into a bare fiberadaptor, used to hold the end of the optical fiber relative to aphotodiode. Hence, the arrangement disclosed by Pen et al. stillrequires an operator to thread the optical fiber from a spool to theclamping assembly and mount the end of the optical fiber into atermination point. Further, operator intervention is still required forsubsequent manufacturing operations, including hermetic sealing,testing, and packaging. Consequently, variations due to operatorhandling still exist.

Hence, the conventional manufacturing process suffers an inherent degreeof variability due to manual handling by the skilled technicians. Inaddition, the necessity of skilled technicians greatly increases themanufacturing costs for the fiber optic devices. Finally, use of skilledtechnicians limits the production capacity, since technicians aresubject to fatigue.

DISCLOSURE OF THE INVENTION

There is a need for an arrangement for the automated fabrication offiber optic devices without the necessity of intervention or supervisionby a human operator or technician.

There is also a need for an arrangement for automated fabrication offiber optic devices, where the handling of optical fibers duringmanufacture is precisely controlled.

There is also a need for an arrangement for the automated fabrication ofa fiber optic device, where an optical fiber can be automaticallyremoved from a spool, threaded, and clamped into a fabrication assemblywithout human intervention.

There is also a need for an arrangement for an automated testing system,where a manufactured fiber optic device can be automatically testedwithout human intervention, and while maintaining the fiber optic endsat precise, controlled positions.

There is also a need for an arrangement for automated fabrication of afiber optic device, where the sequence of drawing optical fiber from aspool, manufacturing the fiber optic device, testing the fiber opticdevice, and packaging the fiber optic device can be performed withoutany human intervention.

There is also a need for an arrangement for automatically forming afiber optic device, where the fiber optic device can be hermeticallysealed as part of the fabrication process without any human interventionor supervision.

There also exists a need for a method for automated fabrication of afiber optic device, where a complete manufacturing process includingpulling fiber from a spool, stripping the optical fiber, forming thefiber optic device, hermetically sealing the fiber optic device, testingand packaging the completed device for shipping, can be performedwithout any operator intervention.

These and other means are attained by the present invention, wherecontrol systems operate and manage the movement of an optical fiberusing a combination of clamps securing the optical fiber, and movablegripping devices that transport the optical fibers during thefabrication process.

According to one aspect of the present invention, a system for automatedfabrication of a fiber optic device includes an interface enclosing anenvironment substantially adapted for manufacture of the fiber opticdevice. The interface includes at least one stationary gripping deviceused to secure an end of a first optical fiber. The first optical fibermay be supplied from a spool positioned outside the manufacturingenvironment. The system also includes first and second stages within themanufacturing environment, each selectively movable along a first axisand comprising at least one clamp mounted to the corresponding stage forsecuring an exposed portion of the first optical fiber. A heat source isselectively positioned between the stages for applying heat to the firstoptical fiber at a selected intensity. A plurality of movable grippingdevices are positioned within the environment and configured tosuccessively transport the end of the first optical fiber from thestationary gripping device to a prescribed position, and to position theoptical fiber for securing by the clamps. At least one detector is usedfor detecting an optical characteristic of the first optical fiber bymeasuring optical energy output at the end of the first optical fiber atthe prescribed position. The system also includes a controller forcontrolling the movement of the first optical fiber by the movablegripping devices. The controller also controls the movement of the firstand second stages and the position and intensity of the heat sourcebased on the detected optical characteristics to form the fiber opticdevice. The movable gripping devices thus transport the optical fiberalong prescribed paths while maintaining control of the end of theoptical fiber. Hence, the optical fiber may be threaded or clamped toany device or apparatus while maintaining control of the end of theoptical fiber. In addition, the movement of the optical fiber by themovable gripping devices from the interface enables the fabrication ofthe optical fiber in an optimum environment specially suited for fiberoptic devices. Hence, the fiber optic device can be manufactured andtested under a carefully controlled system, minimizing the processvariations that might occur in manufacturing. Moreover, operatorintervention is minimized, enabling production capacity to be maximized.

Another aspect of the present invention provides a method of automatingfabrication of a fiber optic device. The method comprises securing anend of a first optical fiber into a stationary gripping device, andtransferring the end of the first optical fiber to one of a plurality ofmovable gripping devices. The end of the first optical fiber is movedalong a prescribed path using at least the one movable gripping device,where the prescribed path coincides with positions of at least onedevice to be threaded by the first optical fiber and primary clampsmounted on first and second stages, respectively. The first opticalfiber is secured to the two primary clamps, and heat is applied on thefirst optical fiber between the two primary clamps with a heat source.The stages are selectively moved along an optical fiber axis to pull theheated first optical fiber at a pulling velocity, and an opticalcharacteristic of the first optical fiber is detected at the end of thefirst optical fiber. The incident heat and the pulling velocity arecontrolled based on a change in the detected optical characteristic inorder to form the fiber optic device. The fiber optic device ishermetically sealed while maintaining a prescribed position of the endof the fiber optic device, and the fiber optic device is secured to atransport device relative to the end of the first optical fiber and acut end of the first optical fiber. The first fiber optic device is thenmoved from the primary clamps and the movable gripping devices whilemaintaining a prescribed position of the end and the cut end of thefiber optic device relative to the transport device.

The dynamic control of the incident heat and the pulling velocity basedon a change in the detected optical characteristic enables the fiberoptic device to be formed in a controlled manner according topredetermined specifications. In addition, the formed fiber optic deviceis hermetically sealed while maintaining the end of the fiber opticdevice in a prescribed position to ensure that the fiber optic devicehas sufficient structural and hermetic protection before being movedfrom the manufacturing area. Finally, use of the transport deviceenables the fiber optic device to be moved for subsequent treatmentwhile maintaining the ends of the fiber optic device at preciselydefined positions relative to the transport device. Hence, maintainingthe precise positions of the ends of the fiber optic device duringtransport enables the fiber optic device to undergo subsequentprocessing during production without introducing any variations orerrors. Consequently, the repeatability of the production system isoptimized, resulting in a minimal number of failure rates or deviationsfrom prescribed specifications.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the attached drawings, wherein elements having thesame reference numeral designations represent like elements throughoutand wherein:

FIG. 1 is a diagram illustrating an overall system for automatedfabrication of a fiber optic device according to an embodiment of thepresent invention.

FIG. 2 is a diagram illustrating in more detail the clamping assembly,the movable gripping devices, and the heat source of the embodiment ofFIG. 1.

FIG. 3 is a diagram showing in detail the left stage and clamp assemblyof FIG. 2.

FIG. 4 is a diagram showing a perspective view of the primary clamp ofFIG. 3.

FIGS. 5A and 5B are top and cross-sectional views of the base portion ofthe primary clamp of FIG. 4, respectively.

FIGS. 6A-6M summarize a method of moving the optical fibers intoposition during fabrication of a fiber optic coupler according to anembodiment of the present invention.

FIGS. 7A and 7B are diagrams illustrating a method of forming a fiberoptic coupler by selectively changing the flame intensity and pull speedbased on detected coupling ratios according to an embodiment of thepresent invention.

FIGS. 8A-8G illustrate a method of hermetically sealing the fiber opticdevice according to an embodiment of the present invention.

FIGS. 9A-9F illustrate an alternative method of hermetically sealing thefiber optic device according to another embodiment of the presentinvention.

FIG. 10 is a diagram illustrating a cross-section of the sealed fiberoptic device of FIG. 9F.

FIG. 11 is a diagram illustrating a transport arm for securing the fiberoptic device before transport according to an embodiment of the presentinvention.

FIG. 12 is a cross-sectional diagram of the optical fiber lead containerof FIG. 11.

FIG. 13 is a front and side view of one of the gripping devices of FIGS.1 and 2 adapted to release the optical fiber.

FIGS. 14A and 14B are diagrams summarizing the movement of the transportarm by a conveyor assembly for moving the fiber optic device from afabrication station to a testing and packaging station.

FIG. 15 is a diagram showing in detail the testing station of FIGS. 14Aand 14B.

FIGS. 16A and 16B are diagrams illustrating alternative implementationsfor the junctions of the optical switching assembly of FIG. 15.

FIG. 17 is a diagram illustrating the optical switches of the opticalswitching assembly of FIG. 15.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a diagram illustrating an overall system for automatedfabrication of a fiber optic device according to an embodiment of thepresent invention. The system 10 enables the automated fabrication offiber optic devices, for example optical attenuators, fiber opticcouplers, etc., without operator intervention. The method of theautomatic fabrication of a fiber optic device may be summarized asfollows.

During fabrication of a fiber optic device, lengths of optical fiber areremoved from a device carrying a length of optical fiber, for example anoptical fiber spool 12. The optical fiber is removed from the spool 12in a manner that prevents twisting of the optical fiber in order toprevent any stresses from being induced on polarization-sensitivefibers, for example birefringent fibers. When the optical fiber spool 12is initially set up for providing optical fiber, the end of the opticalfiber on the spool 12 is secured into a stationary gripping device 14.As described below, the gripping device has at least an open and closedposition, where the optical fiber may move freely when the grippingdevice 14 is in an open position, and where the fiber is securelypositioned when the gripping device 14 is in a closed position.

Once the optical fiber from the spool 12 is secured into the stationarygripping device, the system 10 is able to maintain control over the endof the optical fiber and the path of the optical fiber. Specifically,the end of the optical fiber is controlled at all times to be at aspecified position in order to maintain an accurate relationship betweenthe optical fiber used during fabrication and the associated devicesoperating on the optical fiber. For example, control of the end of theoptical fiber enables the system to automatically clamp the end of theoptical fiber and perform automated fusion splicing, automatedtermination of the optical fiber to a ferrule, automated packaging forshipping in a container that secures the end for future use, etc. Inaddition, the length optical fiber is controlled as it is moved along aprescribed path, enabling the optical fiber to be positioned forclamping and collected for formation of fiber optic leads on each end ofa fiber optic device. Hence, the disclosed embodiment provides acompletely automated system for the fabrication of fiber optic devicesby maintaining at all times precise control over the length of theoptical fiber from the spool 12a and the corresponding fiber end.

Once the end of the optical fiber is secured to the stationary grippingdevice 14a, the optical fiber can be moved along a prescribed path inorder to thread additional devices onto the optical fiber, or toposition the optical fiber with respect to clamping devices. Once theoptical fiber is moved through any devices to be threaded, the opticalfiber is moved along the path of clamp assemblies 16 and 18 mounted onmovable stages 20 and 22, respectively. As described in detail below,the optical fiber is moved in a manner to provide an optical fiber lead24 and 26 on each end of the clamp assemblies 16 and 18.

Once the first optical fiber 10a is clamped for fabrication, the opticalfiber 10a may be pretapered by heating the optical fiber using a movableheat source 32 and pulling the heated optical fiber using the movablestages 20 and 22. The optical fiber leads 24 and 26 are placed in a leadcontainer 28 and 30, respectively, for example trays. A cross-section ofthe lead container is shown in FIG. 12, where members 28a maintain theoptical fiber leads 24.

After any necessary pretapering, a second optical fiber 10b is loadedonto a stationary gripping device 14b. The optical fiber 10b isdespooled from a second spool 12b, at which point the stationarygripping device 14b secures the end of the second optical fiber 10b.Once the end of the second optical fiber 10b is secured to thestationary gripping device 14b, the optical fiber is moved by movablegripping devices along a prescribed path coinciding with positions of adevice to be threaded and the clamp assemblies 16 and 18 supporting thefirst optical fiber 10a. As described in detail below, the secondoptical fiber 10b is also moved in a manner to form optical fiber leads24b and 26b supported by containers 28b and 30b.

Once the first optical fiber 10a and the second optical fiber 10b aresecured in the clamp assemblies 16 and 18, the fiber optic device can bemanufactured according to predetermined specifications, described below.Once formation of the fiber optic device is completed, the fiber opticdevice is hermetically sealed while secured in the clamp assemblies 16and 18. As described below, the clamp assemblies 16 and 18 each includea plurality of clamps that can be successively released and reclamped toenable threaded devices to be moved over the fiber optic device whilemaintaining the position of the optical fibers relative to clampassemblies 16 and 18.

During formation of the fiber optic device, laser energy is supplied tothe optical fibers 10a and 10b by an external laser source thatselectively provides coherent light energy to each of the optical fibers10a and 10b wound on the respective spools 12a and 12b. The laser 34 isunder the control of the control system 36, described below. Theformation of the fiber optic device is controlled by detecting changesin an optical characteristic of at least one of the optical fibers 10using a detector 38. The detector 38 may be directly coupled to one ofthe optical fibers 10, but preferably is coupled to the optical fibers10 via a switching assembly 40, described below. The detector 38 willmonitor the output power of either of the optical fibers 10a and 10b todetermine the coupling ratio. The detector 38 supplies the detectedreading to the control system, which controls the movement of the stages20 and 22 and the intensity of the heat source 32. The control system 36controls the incident heat and pulling velocity on the optical fibers10a and 10b between the set of clamps 16 and 18 based on a change in thedetected optical characteristic. As described below, the dynamicadjustment of the pulling velocity and the incident heat enable thedetected optical characteristic to be controlled such that the desiredoptical characteristic of the fiber optic device to be formed can beachieved.

The fiber optic device is then hermetically sealed, after which thefiber optic device is secured for movement using a transport arm 42,shown in FIG. 11. The transport arm 42 has a pair of gripping devices 44for securing the optical fibers 10. The gripping device 44a secures theoptical fibers 10a and 10b between the optical fiber leads 24a and 24band a movable gripper 72a prior to cutting the optical fiber at acutting point 46a. The gripping device 44b similarly secures the opticalfibers 10 between the leads 26a and 26b and at a prescribed positionrelative to the end of the optical fiber, preferably coincidental withthe cutting point 46b in order to minimize the waste of excess opticalfiber. The transport arm 42 also includes a support member 48 forsupporting the fiber optic device 50, and container support members 52aand 52b for supporting the lead containers 28 and 30, respectively.Hence, the transport arm 42 supports the fiber optic device 50 and theends of the fiber optic device at prescribed positions relative to theends of the fiber optic device using the gripping devices 44a and 44b.Hence, once the optical fibers are cut at the cutting positions 46a and46b, the fiber optic device 50 can be moved while maintaining the endsof the fiber optic assembly at prescribed positions.

Hence, the entire fiber optic device 50 and the associated leads can bemoved while maintaining a precise position of the ends of the fiberoptic device 50. The fiber optic device can then be moved for subsequentprocessing, for example testing and packaging as shown in FIGS. 14A and14B. The fiber optic device 50 may also be moved for subsequentfabrication, for example by integrating the fiber optic device 50 intoother fiber optic devices or assemblies.

As shown in FIG. 11, the transport arm 42 is detachably coupled to acoupling member 54. The coupling member 54 enables the transport arm 42to be moved by a conveyor assembly 56, shown in FIG. 14A, that moves thetransport arm along a first axis to a plurality of stations, for examplethe manufacturing station 58a as shown in FIG. 1, a testing station 58b,shown in more detail in FIG. 15, and a packaging station 58c forpackaging of the fiber optic device for shipment. The conveyor assembly56 also has translational movement in a direction perpendicular to themovement of the transport arm 42, enabling the optical fiber device 50to be transported to any location within a manufacturing area. Once thefiber optic device 50 has been moved to a desired station 58, acorresponding set of clamps at the desired station 58 may be used tosecure the fiber optic device and the corresponding leads to thecorresponding station 58, enabling the transport arm 42 to be releasedfor other use.

If the fiber optic device 50 is transported to a packaging station 58c,shown in FIG. 14b, the transport arm 42 will place the fiber opticdevice and the corresponding leads in a package 60. During packaging,the ends of the fiber optic device are placed in termination plugs 62that secure the ends of the fiber optic device. In addition, the package60 will include lead hooks (not shown) to secure the optical fiber leads24 and 26. Once the optical fiber leads are secured, the lead containers28a, 28b, 30a, and 30b can be removed. In addition, the package 62includes support members 64 for supporting the optical fibers adjacentto the fiber optic device 50. A raised platform within the package 60can support the fiber optic device 50 itself.

Hence, the disclosed embodiment provides an arrangement where a fiberoptic device 50 can be manufactured, tested, and packaged whilemaintaining precise positioning of the ends of the optical fibersforming the end of the manufactured fiber optic device.

FIG. 2 is a diagram showing in more detail the clamping assemblies 16and 18, and the movable gripping devices used to move the optical fibers10 while maintaining a precise control over the end of each of theoptical fibers. As shown in FIG. 2, each of the optical fiber spools 12aand 12b have corresponding optical fibers 10a and 10b that are threadedinto the stationary gripping devices 14a and 14b using despooling arms66a and 66b. Each despooling arm 66 is rotatable about the correspondingspool 12. The despooling arm 66 includes an end gripper 67 capable oflocating and grasping an end of the optical fiber from the spool 12.Once the despooling arm 66 has located the end of the optical fiber onthe spool 12, the end gripper 67 grips the end of the optical fiber, andmoves the end of the optical fiber to the corresponding stationarygripping device 14. Once the optical fiber 10 is secured to thecorresponding stationary gripping device 14, the end gripper 67 remainsin an open position and the despooling arm 66 rotates about the axis ofthe optical fiber spool 12 to remove optical fiber as needed from theoptical fiber spool without adding any twisting or tension to theoptical fiber 10.

If desired, the end clamp 67 at the end of the despooling arm 66 may besubstituted with a ring that merely guides the optical fiber off theoptical fiber spool. In this arrangement, a technician would be neededonly to initially thread the optical fiber 10 from the spool through theloop of the despooling arm 66 to the stationary gripping device 14. Oncethe stationary gripping device 14 secures the end of the optical fiber10, the automated process can take over to form the fiber optic device.If desired, the end of the optical fiber may also be cleaved by a cutter68, shown in FIG. 1, to provide a clean cut at the end of the opticalfiber after the initial threading to the stationary gripper 14.

As shown in FIG. 2, the system includes an interface 70 that encloses anenvironment substantially adapted for manufacture of the fiber opticdevice. The optical fiber spools 12 are positioned in one room, forexample a storage room 71, and the stationary gripping devices 14a and14b are embedded within the interface 70. Hence, once the optical fiberspass through the stationary gripping devices 14, the optical fibersenter an enclosed environment 73, for example a clean room substantiallyfree of dust particles and having a positive pressure of substantiallyoxygen-free atmosphere composed of an inert gas. Hence, the fiber opticdevice can be manufactured in a controlled environment that does notadversely react with the optical fibers before hermetic sealing.

Once the end of each optical fiber 10 is secured to the correspondingstationary gripping device 14, the corresponding end of the opticalfiber 10 is transferred to one of a plurality of movable grippingdevices 72. As shown in FIG. 2, the arrangement of movable grippingdevices 72 includes one set of four gripping devices 72a, 72b, 72c, and72d for moving the first optical fiber 10a along a prescribed path, anda second set of movable gripping devices 72e, 72f, 72g, and 72h formoving the end of the second optical fiber 10b along a prescribed path.As shown in FIG. 2, each of the movable gripping devices 72 are movablealong a track 74. If desired, the movable gripping devices may also bemovable in a direction perpendicular to the track 74, i.e., in both thex and y directions. In addition, each movable gripping device 72 isindependently movable in the vertical (z axis) direction under controlby the control system 36.

Each movable gripping device 72 is independently controllable to gripand release the optical fiber. FIG. 13 shows in detail a front and sideview of the movable gripping device 72. The movable gripping device 72includes a body 76 having a fiber channel 78 and an elastic end 80. Agripper support arm 82 supports the movable gripping device 72 on thetrack 74. The gripping device 72 also includes a closing arm 84rotatably coupled to the body 76 along the y axis. As shown in therighthand portion of FIG. 13, the gripping device 72 also includes aguiding cone 86 having a fiber aperture 88 for the optical fiber. Hence,an optical fiber is secured to the movable gripping device 72 byinserting the optical fiber into the fiber channel 78, and closing theclosing arm on the optical fiber, at which point the optical fiber issecured against the elastic end 80. At the same time, the guiding cone86 guides the end of the optical fiber to the fiber aperture 88. Hence,the movable gripping devices 78 can successively transport the opticalfiber while maintaining the end of the optical fiber by handing off theoptical fiber to an adjacent movable gripping device. Moreover, eachmovable gripping device 78 has an input shape complementary to theguiding cone 86, enabling the optical fiber to be automatically centeredeach time two adjacent gripping devices 72 are engaged to hand off theoptical fiber.

Referring to FIG. 2, the first set of movable gripping devices 72a, 72b,72c and 72d successively hand off the end of the first optical fiber 10aalong a prescribed path to position the optical fiber 10a coincidentwith the clamp assembly 16. The movable gripping devices are alsoconfigured to thread the optical fiber 10a through devices to bethreaded by the optical fibers 10a and 10b, for example an inner tube 90and outer tube 92, supported by tube support members 94 and 96,respectively, to be used during hermetic sealing of the fiber opticdevice. The tube support members 94 and 96 move along the track 74 alongthe optical fiber axis, i.e., in the y direction. The tube supportmembers 94 and 96 also move in the vertical direction (i.e., z axis).

Each of the clamp assemblies 16 and 18 include a plurality of clampsthat enable the optical fibers to be stripped and threaded with theinner tube 90 and the outer tube 92 without losing the position of theoptical fiber relative to the work region between the clamp assemblies16 and 18. The work region includes the movable heat source 32 that ismovable in the x and y direction. According to the disclosed embodiment,a flame source 32a having a separate oxygen supply for operation in theoxygen-free atmosphere is controlled by the control system 36 to have aselectable distance (d) from the optical fibers when secured to theclamp assemblies 16 and 18. Alternative heat sources may be used, forexample a laser heat source, or an electric (thermal) heat source.

As shown in FIG. 2, the tube support members 94 and 96 are supported onthe track 74 along a different path than the tracks used by the movablegripping devices 72. Hence, the movable gripping devices and the tubesupport members 94 and 96 can be moved between each other. For example,the movable gripping devices 72c and 72g can be moved to the right to aposition between the tube support member 96 and the movable grippingdevice 72d without interference.

FIG. 3 is a diagram showing in detail the left stage 20 and the clampassembly 16 of FIG. 2. The movable stage 20 is supported by a surface 98having a plurality of holes 100 for imparting a layer of pressurized gasbetween the stage 20 and the surface 98. Hence, the stage 20 is able tomove along a substantially friction-free surface 98 under the control ofan actuator 102. The actuator 102, controlled by the control system 36of FIG. 1, includes a stepper motor providing high resolution in thetranslational movement of the stage 20 in the y direction, (i.e., alongthe optical fiber axis).

The clamp assembly 16 includes a primary clamp 104 that secures anexposed portion of the optical fibers 10a and 10b for manufacturingwithin the working region between the two stages 20 and 22. The primaryclamp 104 includes a base 104a mounted to the stage 20, and a cover 104bthat engages the base 104a.

FIG. 4 is a diagram showing a perspective view of the primary clamp 104.FIGS. 5a and 5b are top and side views of the base 104a as shown in FIG.4. As shown in FIG. 4, the base 104a includes a slot 106 having a widthcorresponding to the diameter of a bare optical fiber, and a depthcorresponding to 11/2 times the diameter of an exposed optical fiber.Hence, the slot 106 is adapted to accommodate two optical fibers, wherethe second exposed optical fiber sits on top of the first optical fiberand is seated halfway within the slot 106. The first optical fiberinserted into the slot 106 is secured by a first vacuum region generatedby a first series of vacuum holes 108 located at the base of the slot106. The base 104a also includes guiding surfaces 110 for guiding anoptical fiber into the slot 106. The guiding surfaces 110 also include asecond series of vacuum holes 112 for generating a second vacuum regionfor securing the corresponding surface 110a of the clamp cover 104b tothe base 104a.

Hence, an exposed optical fiber is secured in the clamp 104 by placingthe optical fiber within the vicinity of the guiding surfaces 110. Asthe optical fiber is lowered into position of the slot 106, the firstseries of vacuum holes 108 generate a first vacuum region that securesthe first optical fiber within the slot 106. A second optical fiber canthen be added on top of the first optical fiber within the slot 106.After the first and second optical fibers have been inserted into theslot 106, the cover 104b is engaged with the base 104a. The cover 104bengages the base 104a using a support arm 104c fixed to the cover 104b.The cover 104b has a groove 114 corresponding to the second opticalfiber in the slot 106, enabling the first and second optical fibers tobe secured within the clamp 104 upon engagement of the cover 104b withthe base 104a. As recognized in the art, the groove 114 may besubstituted with an extension (not shown) that extends into the slot 106in order to secure a single exposed optical fiber within the primaryclamp 104 upon engagement of the cover 104b with the base 104a. Hence,different covers 104b may be used, depending on whether one or twooptical fibers are to be secured within the clamp 104.

As shown in FIG. 3, the clamp assembly 16 includes clamp 120 and clamps122 and 124. Clamp 120 is similar in structure to the clamp 104, andincludes a base 120a and a cover 120b for securing an exposed opticalfiber. The cover 120b includes a support member 120c for engaging anddisengaging the cover 120b with the base 120a. The base 120a is movablycoupled to the stage 20 via an arm 120d enabling the clamp 120 to movevertically with respect to the stage 20 (i.e., in the z axis).

As shown in FIG. 3, each optical fiber 10 includes a covered portion 126and an exposed portion 128 defined by an optical fiber coating edge 127.The clamps 104 and 120 secure the optical fiber at the exposed portions128, whereas the clamps 122 and 124 secure the optical fibers 10a and10b, respectively, at the covered portions 126. Each of the clamps 122and 124 are independently movable in the y and z axes, and haveremovable covers.

As described below, the clamps 120, 122, and 124 are independentlymovable relative to the stage 20 in order to enable the optical fibers10a and 10b to be appropriately threaded with devices duringmanufacturing of the fiber optic device, described below. For example,if the tube 90 of FIG. 2 needs to be threaded to a working area betweenthe stages, the clamps 104 and 120 can be successively released andreclamped to move the tube 90 while maintaining the secured position ofthe optical fibers 10a and 10b within the working region between the twostages 20 and 22.

Additional details regarding alternative clamping devices may be foundin U.S. Pat. No. 5,395,101 to Takimoto et al., the disclosure of whichis incorporated in its entirety herein by reference.

FIGS. 6A-6M summarize the sequence of forming a fiber optic device usingthe clamp assembly 16 and 18 and the movable gripping devices 72. Thefollowing sequence illustrates one particular example of how thearrangement of FIG. 2 can be used to automate the manufacture of a fiberoptic device while maintaining the path of the optical fiber and theposition of the end of the optical fiber. The process begins in FIG. 6A,where the stationary gripping device 14a hands off the optical fiber 10ato the first movable gripping device 72a. As shown in FIG. 6A, the tube90 supported by the tube support member 94 is positioned between themovable gripping devices 72b and 72c. After the end of the optical fiber10a has been handed off to the movable gripping device 72a, the movablegripping device 72a moves the optical fiber 10a toward the adjacentmovable gripping device 72b along a prescribed path. Before movement ofthe movable gripping device 72a, the stationary gripping device 14 opensto a disengaged position, enabling the optical fiber 10a to move freelythrough the stationary gripping device 14a.

As shown in FIG. 6B, the movable gripping device 72a moves the opticalfiber 10a to the movable gripping device 72b, at which point the movablegripping device 72a hands off the end of the optical fiber to theadjacent movable gripping device 72b for further transport. Once themovable gripping device 72b has received the end of the optical fiberfrom the device 72a, the gripping device 72b secures the end of theoptical fiber 10a for movement. The gripping device 72a releases theoptical fiber 10a to enable the optical fiber to move freely through thegripping device 72a. The gripping device 72b then moves in the rightdirection (i.e., along the y axis), while the gripping device 72a movesin the rightward direction at a distance behind the gripping device 72bcorresponding to the length of the tube 90, as shown in FIG. 6C. Oncethe gripping device 72b reaches the edge of the tube 90, the grippingdevice 72a closes on the optical fiber 10a. The gripping device 72b thenopens, enabling the gripping device 72a to push the optical fiber 10athrough the tube 90.

Once the gripping device 72a reaches the adjacent gripping device 72b,the gripping device 72c, under the control of the control system 36,captures and secures the end of the optical fiber 10a as the opticalfiber 10a passes through the tube 90. Once the gripping device 72csecures the end of the optical fiber 10a, shown in FIG. 6D, the grippingdevices 72a and 72b release the optical fiber 10a.

As shown in FIG. 6E, the gripping device 72c then moves the opticalfiber 10a along a prescribed path corresponding to the second clampassembly 18 while maintaining the end of the optical fiber 10a. At thesame time, the threaded tube 90 is moved by the tube support member 94to a position between the clamps 120 and 122 of the first clamp assembly16. The gripping device 72c moves the optical fiber to the grippingdevice. 72d, and hands off the optical fiber 10a to the gripping device72d. The gripping device 72d secures the end of the optical fiber 10a,ensuring that the end of the optical fiber 10a is controlled at alltimes. Alternately, the gripping device 72d may pass the end of theoptical fiber to a splicer 130, shown in FIG. 1. The splicer 130 has asplicer clamp 132 that is adapted to receive the end of the opticalfiber from the gripping device 72d, clamp the end of the optical fiber,and splice the end of the optical fiber 10a to a lead of the switchingassembly 40.

Once the optical fiber 10a is secured by the gripping device 72d, thegripping devices 72c and 72d cooperate to form the optical fiber lead 26to the right of the clamp assembly 18, as shown in FIG. 1. Once thegripping devices 72c and 72d have pulled a sufficient length to form theoptical fiber lead 26a, for example 1, 5 or 10 meters, the grippingdevices 72a and 72b cooperate to form the optical fiber lead 24a, shownin FIG. 6F.

Once the leads 26a and 24a have been formed in FIG. 6F, the clamps 122and 122' of the clamping assemblies 16 and 18, respectively, are movedvertically with respect to the respective stages 20 and 22 to clamp ontothe covered portion of the optical fiber 10a. Once the covered opticalfiber 10a is clamped by the clamps 122 and 122', as shown in FIG. 6G, astripping region 134 between the clamps 122 and 122' can be stripped bya stripping device 136 having a support member 136a coupled to the track74 for movement along the optical fiber 10a. The stripping device 136may strip the coating from the optical fiber using chemical etchtechniques or heating techniques. After stripping the coating from theoptical fiber in FIG. 6G, the optical fiber has an exposed portion 128bounded by the coating edges 127, as shown in FIG. 6H. The exposedportions of the optical fibers are then clamped by clamps 120 and 120',which are raised by the corresponding arms 120d to secure the exposedoptical fiber. Once the exposed optical fiber is secured by the clamps120 and 120' of the respective clamp assemblies 16 and 18, the clamps122, 120, 120', and 122' and the tube 90 are lowered simultaneously toplace the optical fiber 10a into the clamps 104 and 104' that are fixedto the stages 20 and 22, respectively. Once the optical fiber is securedin the clamps 104 and 104' as shown in FIG. 6I, operations such aspretapering may be performed on the optical fiber 10a. In addition, ifthe fiber optic device to be formed is an optical attenuator consistingof a single optical fiber, the optical fiber attenuator would be formedat this time.

If a second optical fiber is to be threaded, for example for theformation of a fused biconical tapered coupler, the second optical fiber10b would be threaded through the tube 90 in a manner described withrespect to FIGS. 6A-6F, resulting in the arrangement of FIG. 6J. Duringthreading of the second optical fiber 10b, clamps 120 and 104 secure theoptical fiber 10a, while the clamp 122 releases the optical fiber 10a.The clamp 120a is then slightly accommodated to enable the tube 90 to bepartially moved to accommodate the threading of the second optical fiber10b. After the second optical fiber 10b has been threaded as shown inFIG. 6J, the clamps 124 and 124' clamp the covered portion of theoptical fiber 10b to perform stripping of the optical fiber 10b. Afterstripping has been performed, the optical fibers 10a and 10b are clampedas shown in FIG. 6K, at which point fusion of the optical fibers 10a and10b is performed to form a fiber optic device 140, described below.After formation of the fiber optic device as shown in FIG. 6L, theoptical fibers 10a and 10b are unclamped from the clamp 104 to enablethe tube 90 to be moved by the tube support member 94 to cover the fiberoptic device 140. During the time that the clamps 104 and 104' are in anunclamped position, the clamps 120 and 120' remain clamped to maintainthe accurate position of the optical fibers. Once the tube 90 is movedto a position enclosing the fiber optic device 140, the clamps 104 and104' can be reclamped in order to perform the subsequent steps ofhermetically sealing the fiber optic device 140, described below.

FIGS. 7A and 7B are diagrams summarizing the method of forming a fiberoptic device by dynamically adjusting the pulling speed and heatintensity to control the detected coupling ratio. According to thedisclosed embodiment, the pulling speed and the heat intensity aredynamically controlled by the control system 36 in accordance withdetected coupling ratio to control the rate of change in the couplingratio. Hence, the coupling ratio of a fiber optic device beingmanufactured can be controlled based on dynamically adjusting the heatintensity and pulling speed. The method begins in step 160 by initiallysetting up the apparatus as shown in FIG. 1, where optical fibers 10aand 10b are connected to the clamping assemblies, described above, andthe ends of the optical fibers 10a and 10b are connected to a switchingassembly that uses a detector 38 to dynamically monitor the output ofthe ends of the optical fibers 10a and 10b. The optical fibers 10a and10b are then secured to the clamps, as described above, with sufficientinitial tension to straighten the optical fibers to ensure that theoptical fibers contact each other within a fusion region. Once the setupis completed according to the arrangement of FIG. 1, an initialmeasurement is taken by the detector 38 in step 162. The couplerformation process then begins in step 164 by applying heat to theoptical fibers 10a and 10b. The heat is applied at a predeterminedinitial intensity, for example by placing a flame generated by the heatsource 32a at a predetermined distance (d=d₀) from the optical fibers,for example by placing the tip of the flame directly on the fibers.

Once the optical fibers 10a and 10b have softened, the controller 36starts pulling the optical fibers in step 166 at an initial velocity ofv_(p) =v₀, where v₀ equals, for example, 5 mm per minute. The initialdistance of the heat source (d₀) and the initial pull speed (v₀) aremaintained until the controller 36 detects in step 168 a substantialchange in the detected coupling ratio of between 3% to 5%. Thesubstantial charge in the coupling ratio identifies the transition pointat which the optical fibers begin to optically couple the transmittedlaser energy.

If the coupling ratio is allowed to increase by maintaining a constantpull velocity and a constant heat intensity, the coupling ratio maycontinue to increase uncontrollably. It has been discovered that therate of increase in the coupling ratio increases substantially after thecoupling ratio reaches 10%. Hence, the control of the coupling ratioshould begin before the coupling ratio reaches 10%.

The control of the coupling ratio begins in step 170 by decreasing thepull speed at a specified deceleration rate a_(p) (t). The couplingratio is then controlled in step 172 by moving the heat source 32a awayfrom the optical fibers 10a and 10b at a speed of v_(f) (t). The initialposition of the heat source 32a is necessary to soften the opticalfibers sufficient to overcome the surface tension of the optical fibers.Once the optical fibers begin to physically fuse, the incident heat onthe optical fibers is reduced by moving the heat source away from theoptical fibers. To prevent movement of the heat source 32a from causinga change in the shape of the taper in the coupler, the pull speed issimultaneously reduced such that the ratio between the heat intensityand the pull speed is substantially constant. Hence, reducing the flamereduces the rate of change in the coupling ratio when the pull speed isreduced accordingly. Moreover, a reduction in heat intensity ensures thecoupling ratio readings are not distorted.

Hence, by reducing the heat intensity until the point where the opticalfibers are soft enough to be pulled, the method of forming the couplermay be precisely controlled.

After the pull speed and the heat intensity have been changed in steps170 and 172, respectively, the coupling ratio (CR) is checked atselected wavelengths. If desired, the controller 36 may also calculatein step 174 the rate of change in the coupling ratio. After calculatingthe coupling ratio at the selected wavelengths and the rate of change inthe coupling ratio, the controller 36 decides in step 176 whether theheat reduction rate (a_(f)) or the deceleration (a_(p)) of the pullspeed needs to be changed in step 178. If no change in the decelerationrate is needed, the controller 36 returns to step 170 to selectivelydecrease the pull speed and the flame velocity for the next iteration.According to the disclosed embodiment, the decreases in steps 170 and172 are implemented in one second iterations.

FIG. 7B is a diagram illustrating the change in the coupling ratio,where a coupling ratio curve 210 increases steadily until reaching adesired level 212. As described above, the heat source is preferablygradually reduced before reaching the desired coupling ratio 212 toensure any sudden changes in the heat intensity do not distort thecoupling ratio readings. Hence, the final incremental changes in thecoupling ratio along the curve 210 is accomplished by maintaining theheat source at a reduced intensity sufficient to enable the opticalfibers to be pulled, steadily decreasing the pull speed (v_(p)) untilthe desired coupling ratio level 212 is reached, at which point the pullspeed (v_(p)) is set to zero and the heat source is removed withoutcausing a change in the coupling ratio.

The disclosed method thus provides full control over the changes in thecoupling ratio by dynamically adjusting the heat intensity and thepulling velocity. In addition, once the heat intensity has been reducedby a sufficient amount, i.e., once the flame has been moved far enoughaway, accurate measurements of the coupling ratio may be obtained, suchthat the pulling process may be held to precisely at the desiredcoupling ratio. Hence, the heating and pulling process can beautomatically controlled to form a fiber optic device having a precisecoupling ratio according to predetermined specifications. Additionaldetails regarding the method of forming a fiber optic device bydynamically changing heat intensity and pull speed based upon thedetected optical characteristics can be found in co-pending applicationSer. No. 08/718,727, filed Sep. 24, 1996, entitled "Method and Apparatusof Forming a Fiber Optic Coupler By Dynamically Adjusting Pulling Speedand Heat Intensity," (Attorney Docket 2986-002), the disclosure of whichis incorporated in its entirety herein by reference.

FIGS. 8A-8G summarize the method of hermetically sealing the fiber opticdevice 140 according to an embodiment of the present invention.

As shown in FIG. 8A, the fiber optic device 140 is surrounded by asubstrate 404a and 404b, each having a trough to accommodate the fiberoptic device and the optical fibers. The substrates 404 are preferablyformed of fused quartz and having a surface layer consisting essentiallyof aluminum. The substrates 404 are brought together, for example, usingexternal support arms 405, to form the enclosure 430 shown in FIG. 8B. Apair of end rods 432 are then moved toward the end portions 414a and414b, which align the substrates 404a and 404b along the fiber opticaxis in FIG. 8C. In addition, the end rods 432 maintain the enclosure430 while the support rods 405 are removed.

As shown in FIG. 8D, a sleeve 434 consisting essentially of purealuminum is then threaded over the enclosure 430. The sleeve 434 has aninner diameter slightly greater than the outer diameter of enclosure 430and a length slightly greater than the enclosure 430.

As shown in FIG. 8E, two molds 440a and 440b engage the outer diameterof the sleeve 434. The mold portions 440a and 440b each havesemi-circular shapes along their axial lengths and a center section 446spaced from the outer diameter of the sleeve 434 and end portions 448 incontact with the ends of the sleeve 434. The edges 452 are disposedaxially outwardly from the middle body portion of the enclosure 430.

The mold portions 440a and 440b exert sufficient pressure on the sleeve434 to maintain the position of the sleeve 434 and the enclosure 430,enabling the end rods 432 to be moved as shown in FIG. 8F without movingthe substrates 404a, 404b, or the sleeve 434.

Each of the mold portions 440a and 440b include heating elements,causing the sleeve 434 and the aluminum surfaces of the substrates 404to be heated to just below their corresponding melting point, at whichpoint the molds 440a and 440b compress the metal sleeve to form ahermetic seal around the enclosure 430 and the enclosed optical fibers.Heating of the tubing 434 to just below its melting point causes thetubing 434 and the surface metal layers of the substrate 404 to begin tofuse together during the heating and compression by the mold portions440a and 440b. As the aluminum cools, the aluminum surfaces and thetubing 434 fuse together and compress to form a compressive seal aroundthe quartz portion of the enclosure 430 and the enclosed fiber opticdevice 140, forming the hermetically sealed device 460 of FIG. 8G.

Additional details regarding the method of hermetically sealingaccording to FIGS. 8A-8G are disclosed in co-pending application Ser.No. 08/763,052, filed even date herewith, now U.S. Pat. No. 5,805,757entitled "Fiber/Optic Device Hermetically Sealed by Heating andCompressing Metal Seals and Method for Making the Same," (AttorneyDocket No. 2986-005), the disclosure of which is incorporated in itsentirety herein by reference.

An alternative technique of hermetically sealing the fiber optic deviceis disclosed in co-pending application Ser. No. 08/679,059, filed Jul.12, 1996, now U.S. Pat. No. 5,680,495, entitled "Fiber Optic DeviceHermetically Sealed by Compressed Metal Seals and Method for Making theSame," (Attorney Docket No. 2986-001), the disclosure of which isincorporated in its entirety by reference. FIGS. 9A-9F correspond toFIGS. 8A-8F of that application disclosing an alternative method forhermetically sealing the fiber optic device. As shown in FIG. 9A, thefiber optic device 140 has metal seals 300a and 300b formed on each sideof the optical fiber, for example by using molds to inject moltenaluminum onto the optical fiber. As the molten aluminum cools, thealuminum bonds with the optical fibers, and forms a compressive seal onthe optical fibers. Once the metal blocks 300 are formed, an enclosure302 composed of upper and lower portions 304 are placed surrounding themetal seals 300. Each of the portions 304 are preferably quartz-bodieshaving a first surface layer of pure aluminum and an outer layer ofgold. The portions 304 include a trough running along the optical fiberaxis, that provides a spaced enclosure for the optical fibers and thefiber optic device 140. In addition, the internal aluminum and goldlayers of the portions 304 engage the metal blocks 300a and 300b to forma secure seal when compressed, as shown in FIG. 9C. The enclosure 302 ispreferably assembled in an oxygen-free atmosphere, for example anatmosphere having a positive pressure of nitrogen, helium or argon.

After formation of the enclosure 302, a tubing 306 is threaded over theenclosure 302, shown in FIG. 9D. The tubing 306, formed of fused silica,includes a deformable metal interface layer, such as the aluminum/goldinterface layer on the inner and outer surfaces of portions 304a and304b. The tube 306 has an inner diameter which is slightly less than theouter diameter of the enclosure 302. Hence, the deformable metalinterface layer on the inner surface of tubing 306 interacts with thedeformable interface layer on the outer surface of the enclosure 302 toform a gas-tight enclosure exerting a compressive force on the enclosure302. The gas-tight enclosure is formed by the displacement of therespective deformable metal layers. The tubing 306 exerts a compressiveforce to provide additional sealing between the tubing 80 and thesubstrates 304a and 304b of the enclosures and to provide compressiveforce to maintain the hermetic seal between the substrates 304a and 304band the metal block 300. Ultrasonic welding may also be used to seal thecontacting metal layers.

After sealing the tubing 306 as shown in FIG. 9D, gold caps 308 areadded onto each end of the tubing 306 to cover the ends of the tubing306, and the ends of the metal seals 300. The gold caps 308 consistessentially of gold. The caps 308 may be prethreaded on the opticalfibers, or may be attached by crimping a sheet of gold metal at eachend. As the gold caps 308 are compressed at each end of the tubing 306,the portions of the metal blocks 300 extending from the tubing 306 arepartially deformed with the caps 308. The exposed optical fibers arethen coated with a conventional sealing material 310, for examplerubber, as shown in FIG. 9E.

After the exposed optical fibers have been covered by the sealant 310, aprotective metal tubing 312, formed of a nickel-based alloy, forexample, Invar, is threaded over the assembly. If desired, a non-metaltubing having a relatively low thermal expansion coefficient may also beused. After loosely fitting the metal coating 312 over the assembly, themetal coating 312 is secured by injecting into the space between metalcoating 312 and the assembly a sealant, for example, an RTV (roomtemperature vulcanizing) silicon coating 314.

After the fiber optic device 140 has been hermetically sealed to formthe hermetically-sealed fiber optic device 50, the completed fiber opticdevice 50 can be moved as described above with respect to FIGS. 11 and14 for testing.

FIG. 10 is a cross-section of the hermetically sealed device taken alonglines I--I of FIG. 9F. FIG. 10 shows the portion of the body 304a havingan internal quartz body with an interface layer 305 fused between thequartz portions 304a and 304b. As shown in FIG. 10, the metal interfacelayer 305 surrounds the quartz portion of the bodies 304a and 304b andforms an interface layer between the quartz bodies and the tubing 306.In addition, the metal block 300a encapsulates the optical fibers 10,forming a hermetic seal for the fiber optic device 140 enclosed by thehermetic seal.

After hermetic sealing, a transport arm 42 is connected to the fiberoptic device 50, as described above with respect to FIG. 11, and thefiber optic device 50 is transported to a testing station 58b as shownin FIG. 14B. As shown in FIGS. 14A and 14B, the testing station 58bincludes a set of clamps 228, and splicers 229 for splicing the ends ofthe optical fibers to leads 232 from an optical switching assembly 230.

FIG. 15 is a diagram illustrating in detail the testing assembly 58b ofFIGS. 14A and 14B including the switching assembly 230. The splicers 229splice the ends of the optical fiber from the fiber optic device 50(referred to herein as leads 10a, 10b, 10c, and 10d) to the leads 232 ofthe optical switching assembly. After the fiber optic leads of the fiberoptic device 50 are fusion spliced to the optical switching assembly 230by the splicers 229, the switching assembly 230 selectively establishesoptical paths between a test laser 314 and a detector 316 to verify theoptical performance of the device under test, namely the fiber opticdevice 50.

As shown in FIG. 15, the optical switching assembly 30 includes two 1×Nswitches 222a and 222b, a first group of optical fibers 234, a secondgroup of optical fibers 236, and a plurality of junctions 238.

FIGS. 16A and 16B are diagrams illustrating alternative implementationsof the junctions 238 of FIG. 15. The junction 238 of FIG. 16A isimplemented as an optical 1×2 switch 244 that selects between one of thefirst group of optical fibers 234 and the second group of optical fibers236 for connection with the corresponding lead 232. The junction 238 mayalso be implemented as a passive coupler 246, shown in FIG. 16B, thatconnects one of the optical fibers from each group 234 and 236 with thecorresponding lead 232.

FIG. 17 is a block diagram illustrating in detail one of the switches222 of FIG. 15. The switch 222 is preferably a 1×N switch, where thecontrol system 36 of FIG. 1 selectively connects a terminal end, forexample lead 240, to one of the first group of optical fibers 234. Anexemplary optical switch is the commercially available fiber opticswitch by DiCon Fiber Optics, Inc., Berkeley, Calif., Model No. MC601.The switch 222 has a maximum insertion loss of -1.3 dB (-0.6 dBtypical), and a maximum back reflection of -55 dB (-60 dB typical) atwavelengths of 1310 and 1550 nm (broadband). Short term repeatabilityshould be +/-0.005 dB. Each of the optical fibers 234 connected to theswitch 222 are terminated within the switch 222 by a Graded RefractedIndex (GRIN) rod lens 251 that provides minimal insertion loss andmaximum coupling efficiency. Each optical fiber is also angled andcoated with an anti-reflective coating to minimize back reflectance inthe event that the particular optical fiber 234 is not connected to theoptical fiber 240 by the switch 222. The GRIN lens 251 is preferably aquarter-wavelength (0.25) pitch.

As shown in FIG. 15, the fiber optic device 50 is connected to theoptical fiber leads 232 of the optical switching assembly 230 by fusionsplices after the ends are secured to the clamps 228a and 228b. Eachlead 10 of the fiber optic device is connected to a corresponding leadof one of the junctions 238 of the optical switching assembly 230. Thelaser 314 is connected to the switch A 222a via an optical fiber 240,and the detector 316 is connected to switch B 222b via an optical fiber242. All fibers are preferably single mode fibers.

Once the fiber optic device 50 is connected to the switching assembly230, the switches 222 are controlled so that the laser 314 supplieslaser energy to only one of the first group of optical fibers 234, andthe detector 316 receives transmitted light energy from only one of thesecond group of optical fibers 236. For example, assuming that switch Awas set to route light received from the light source 314 to thejunction 238a, and switch B was set to route light received fromjunction 238a to the detector 316, the test assembly would be able toautomatically determine the back reflectance of light from lead 10b ofthe fiber optic device 50 via the lead 232a. After testing for backreflectance, the coupling ratio of leads 10c and 10d relative to lightinput to lead 10b can be determined by successively setting the switch Bto transmit light to the detector 316 light received from lead 232c,measuring the detected light, and then switching the switch B 222b toroute the light from lead 232d to the detector 316. In addition,near-end crosstalk of the coupler SO can be determined by maintainingswitch A 222a to input light to the lead 232a, and setting the switch B222b to route light received from lead 232b to the detector 316.

Hence, the optical fiber device S0 can be tested in any desired mannerwithout the necessity of disconnecting and reconnecting leads to theoptical fiber device. Variations in the coupling losses in the opticalfiber assembly 230 may be quickly identified before each test byswitching the optical switches 222a and 222b to junctions 238i and 238jhaving leads 232i and 232j fusion spliced with a single optical fiber260, also referred to as a loopback fiber, that enables the detector 316to quickly measure the loss of the optical switching assembly 230, oroptical characteristics of the laser 314, for example laser power,wavelength, polarization state, etc. Variations can be detected bycomparing the detected value of the loss during connection to theloopback fiber 260 with previously-stored values. Variations can also bedetected by switching the optical switches 222a and 222b to lead 232e,which is terminated with a commercially-available external referencereflector (-35 to -40 dB) (not shown). Alternately, the end of fiber232e can be cleaved by scoring the fiber end using a diamond tipperpendicular to the length of the fiber.

Additional details found in co-pending application Ser. No. 08/725,641,filed Oct. 1, 1996, now U.S. Pat. No. 5,764,348, entitled "OpticalSwitching Assembly for Testing Fiber Optic Devices," (Attorney DocketNo. 2986-003), the disclosure of which is incorporated in its entiretyby reference.

According to the present invention, a method for making fiber opticdevices is completely automated to maximize production efficiency,yield, and reliability. The automated arrangement for making fiber opticdevices includes the threading of optical fibers from spools, making thefiber optic device, hermetically sealing the fiber optic device, testingthe fiber optic device, and packaging the fiber optic device forshipment. The entire manufacturing process can be controlled by acentral controller, or individual controllers that communicate betweeneach other via a local area network.

The disclosed embodiments may also be modified to perform additionaloperations prior to packaging a fiber optic device. For example, thetesting station 58b may be supplemented or substituted with a long-termreliability testing station, where a plurality of fiber optic devicesundergo long term testing in a stressed environment having hightemperatures and high humidity to determine long term opticalperformance. Alternately, the fiber optic devices may be sent to astation that automatically terminates the ends of the optical fiberswith fiber optic connectors such as ferrules. An exemplary arrangementfor terminating optical fibers that could be implemented in thedisclosed automated system is disclosed in copending application No.08/763,125, filed on even date herewith, now U.S. Pat. No. 5,815,619entitled "Fiber Optic Device Hermetically Sealed Using Only Aluminum"(Attorney Docket 2986-004), the disclosure of which is incorporated inits entirety by reference.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiment, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

I claim:
 1. A method of automating fabrication of a fiber optic device,comprising:securing an end of a first optical fiber into a stationarygripping device; transferring the end of the first optical fiber to oneof a plurality of movable gripping devices; moving the end of the firstoptical fiber along a prescribed path using at least the one movablegripping device, the prescribed path coinciding with positions of atleast one device to be threaded by the first optical fiber and primaryclamps mounted on first and second stages, respectively; securing thefirst optical fiber to the two primary clamps; applying incident heat onthe first optical fiber between the two primary clamps with a heatsource; selectively moving the stages along an optical fiber axis topull the heated first optical fiber at a pulling velocity; detecting atthe end of the first optical fiber an optical characteristic of thefirst optical fiber; controlling the incident heat and the pullingvelocity on the first optical fiber, based on a change in the detectedoptical characteristic, to form the fiber optic device; hermeticallysealing the fiber optic device while maintaining a prescribed positionof the end of the fiber optic device; securing the fiber optic device toa transport device relative to the end of the first optical fiber and acut end of the first optical fiber; and moving the fiber optic devicefrom the primary clamps and the movable gripping devices whilemaintaining a prescribed position of the end and the cut end of thefiber optic device relative to the transport device.
 2. The method ofclaim 1, wherein the moving step comprises:moving the end of the firstoptical fiber along a first segment of said prescribed path using theone movable gripping device; handing off the end of the first opticalfiber from the one movable gripping device to a first adjacent movablegripping device; moving the end of the first optical fiber along asecond segment of said prescribed path and through the at least onedevice to be threaded using the adjacent movable gripping device; andhanding off the end from the adjacent movable gripping to a secondmovable gripping device adjacent to the first adjacent movable grippingdevice.
 3. The method of claim 1, wherein the first optical fiber is acoated optical fiber, the method further comprising:securing the coatedfirst optical fiber to secondary clamps movably positioned on the firstand second stages, respectively, the primary clamps on the first andsecond stages positioned between the corresponding secondary clamps;stripping the coated optical fiber to expose a segment of the opticalfiber; and wherein the primary clamps securing step comprises securingthe exposed segment of the first optical fiber to the two primaryclamps.
 4. The method of claim 3, further comprising:securing an end ofa second coated optical fiber into a second stationary gripping device;transferring the end of the second coated optical fiber to one of asecond plurality of movable gripping devices; moving the end of thesecond coated optical fiber along at least a portion of said prescribedpath including said at least one device and said primary clamps;securing the second coated optical fiber to a second set of secondaryclamps movably positioned on the first and second stages, respectively,the primary clamps on the first and second stages positioned between thecorresponding second set of secondary clamps; stripping the secondcoated optical fiber to expose a segment of the second optical fiber;and securing the exposed segment of the second optical fiber to the twoprimary clamps.
 5. The method of claim 1, wherein the primary clampssecuring step comprises:placing an exposed portion of the first opticalfiber within each of the primary clamps; imparting a suction force onthe first optical fiber within each of the primary clamps; covering eachof the primary clamps with a clamp housing having a segment forengagement with the exposed portion of the optical fiber; and impartinga second suction force on each clamp housing from the correspondingprimary clamp.
 6. The method of claim 1, further comprising:securing thefirst optical fiber to secondary clamps movably mounted on the first andsecond stages, the primary clamps positioned between the secondaryclamps; releasing the first optical fiber from one of the secondaryclamps; moving the threaded device along the first optical fiber andacross the one released secondary clamp to a position between thereleased secondary clamp and the corresponding primary clamp; reclampingthe first optical fiber in the released secondary clamp; releasing thefirst optical fiber from the primary clamp adjacent to the movedthreaded device; moving the threaded device along the first opticalfiber and across the one released primary clamp to a position betweenthe primary clamps; and reclamping the first optical fiber in thereleased primary clamp.